Though the activewear trend is still firing on all cylinders, there have been some recent green shoots in the blue jean market. Just last week, GapCEO Art Peck told investors that the company is "seeing a little bit of life" in denim.

His comments followed optimistic remarks from Levi's CEO Chip Bergh on its earnings call last month, when he said new products and a revitalization on the runways is breathing freshness back into the category.

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A customer browses jeans at a Gap Inc. store in San Francisco.

At VF Corp, parent of Lee and Wrangler, fourth-quarter jeanswear sales rose 3 percent to $755 million, outpacing flat revenues in the category for the full year. They were helped by improving trends in the Americas.

And in February, bullish commentary from participants at a trade show in Las Vegas caused Guggenheim Partners analyst Howard Tubin to suggest "there may be hope for denim" in coming months.

"When speaking to people at the [MAGIC trade] show, we were encouraged to hear about newness in the category that could provide a spark to the business in the coming months," he wrote in a note to investors. "The 'boyfriend' and 'girlfriend' styles appear to be gaining traction, as well as the flare bottom."

Total U.S. jean sales declined 8 percent on a dollar basis in 2014, to $15.4 billion, according to The NPD Group/Consumer Tracking Service. The category's struggles were reflected in sales shortfalls at Gap, where the assortment is heavily skewed toward denim. In 2014, same-store sales for the Gap brand fell 5 percent compared to the prior year.

Analysts don't expect trends to pick up at the label until at least the holidays, when the influence of new product design head Wendi Goldman hits the selling floor. They were more optimistic, however, about momentum in denim.

"Upside in denim may be seen sooner than the overall assortment as denim has been recently well received," Cowen and Co. analyst Oliver Chen wrote in a note to investors.

As for Gap's Old Navy brand, which has been posting robust sales growth, "There are so many options when it comes to wearing denim right now," said Jill Stanton, executive vice president of product development and design. "We are seeing consumers' appetites for all different kinds of silhouettes—boyfriend, straight, overalls, shorts, skinny, flares. This is great news for retailers."

There's also been a shift on the runways. According to trend forecasting firm WGSN, activewear isn't as prevalent on the catwalk as it had been the past few seasons; in its place, premium denim is starting to gain traction, WGSN's head of denim and youth Amy Leverton said.

While that will take some time to trickle down to the mass market, where denim has been particularly challenged, it does push innovation and excitement in the category, she said.

"The main shift in the market that I can see is that designers are using denim," Leverton said.

'Athleisure' isn't going anywhere

Although Peck said he's "encouraged" by the conversation around denim, he cautioned it's too soon to call it a turn. For his part, Tubin's recent store checks found that while the majority of products at American Eagle were marked as full-price, denim was selling at a $10 discount.

What's more, shoppers are still snatching up jogger-style bottoms and yoga pants, driving dollar sales of women's activewear 8 percent higher in 2014, according to The NPD Group/Consumer Tracking Service.

But the shift isn't limited to women's wear—it's also trickled down to the children's market, said Ellen Kirkhope, head of kidswear at trend forecasting firm WGSN. Whereas U.S. dollar sales of adult jeans declined 7 percent last year, sales for kids, infant and toddler jeans dropped 15 percent, NPD's data showed.

"The jersey denim that's so popular now is becoming such a mainstay staple for kidswear because it's more comfortable," she said. She added that there is always a delay in the trickle down of trends from women's and men's into children's wear, indicating the comfort trend will be here to stay for some time.

To combat this overall market shift, Levi's new women's lineup fuses shoppers' desires for comfort with its traditional denim offerings. The firm worked on the line for about 18 months, and Bergh said it has a "good focus on soft, stretchy product, which is where the consumer has gone."

"We've done a ton of research on this. It's been very well received," he told investors.